1. Field of the Invention
This invention relates to methods and devices to coordinate drive systems of rail-guided vehicles with individual-wheel drive.
2. Description of the Prior Art
Since the early 1990s, many manufacturers of streetcars have been offering vehicles with a continuous low floor (100% low-floor vehicles). The difficulty in the development of these low-floor railway vehicles was that the wheel set axle used in the earliest models extended through the passenger compartment and was therefore not compatible with the low-floor concept. One solution that most of the manufacturers adopted was to replace the wheel set axle with individual-wheel suspension and an individual-wheel drive system.
Wheel set axles, the track wheels of which have a conical wheel profile, have the natural tendency, when there is a lateral offset or mismatch of the wheel set, to automatically turn away from the center of the track, i.e. to execute a pivoting or turning movement around the vertical axis. They are therefore able both to prevent continuous unilateral striking of the flange against the rail head by a wheel in a straight track without external support, and also, for the radial adjustment of the wheel set axle to the center point of the track curve, to execute the necessary turning movements themselves without external steering assistance. This natural advantage of the track guidance principle of the wheel set is simultaneously its greatest disadvantage.
The ability of the wheel set to turn independently means that a wheel set that was once caused to execute a turning movement in a straight track, continues to execute uncontrolled and continuously alternating turning movements. It thereby moves on a wave-shaped path (sine curve) through the track channel of the track. Undesirable skewing and a constant alternation of drive and braking forces at the wheel-rail contact points of the track wheels are the cause of a rough ride of the vehicle. Wear on the track wheels and the rails as well as loud running noises are the logical consequences. The movements of the wheel set can thereby become so great that they result in derailments.
Unconnected wheel pairs, on the other hand, are not capable of self-steering, as a result of which they are unsuitable for travel around curves.
DE 195 40 089 A1 describes a method for the safe and low-wear guidance of vehicles along a specified course in which the steering movements necessary to keep to the course are produced by drive and braking torques of the same magnitude but in opposite directions, which result in the steering moments necessary for steering. This method is used to actuate the drive wheels when the vehicle is traveling around curves.
DE 195 38 379 C1 describes a two-wheel truck with individual-wheel drive for track-guided vehicles with controlled steering, in which the truck for each wheel carrier has two vertical swivelling axes that are each located outside the wheel-rail contact points, whereby in alternationxe2x80x94with an arresting of the position of the swivelling axis that is currently outside the curvexe2x80x94the wheel carrier is pivoted around precisely this axis.
DE 41 35 691 A1 describes a method for the regulation of vehicles with individual-wheel drive and brake modules which, in addition to achieving optimum utilization of the adherence and preventing slip/stick effects, can act to assist guidance. In this case, each drive module has its own closed-loop torque control circuit, with an estimating element for the determination of the current value of the torque, whereby the closed-loop torque control circuits are coupled to each other by means of a plurality of minimum value stages to eliminate the lateral forces.
EP 0 511 949 B1 describes a method for the control of a truck without rigid axle connections, in which at least two of the track wheels opposite one another are driven individually by separately actuatable drive units, and in which, when the vehicle is traveling around a curve, the drive units of track wheels opposite each other are operated at different outputs, whereby above a minimum speed of 10 km/h, in particular when the vehicle is traveling straight ahead, the power output of the drive units of the track wheels opposite each other is periodically increased and decreased within defined bandwidths, whereby the change in the power output of the track wheels opposite each other is done in phase opposition.
EP 0 590 183 B1 describes a method to improve the running characteristics of a truck that is provided with a plurality of individual wheels on a railway vehicle, the traction motors of which are fed by wheel blocks by means of two control and regulation devices. The speeds of rotation of the wheels are used to determine two wheel block speeds of rotation, from which a current speed differential is formed and compared with a predetermined speed differential set point. As a function of this negative deviation, a control output is then generated which, by addition or subtraction of a control lever set point, forms a torque set point for the respective wheel block. The speed differential set point is determined exclusively for one wheel block as a function of a determined radius of curvature and of the truck speed.
The object of this invention is to create a vehicle and a method to coordinate the drive of rail-guided vehicles with individual-wheel drive on straight and curved tracks, in which it becomes possible to travel through curves with minimum wear and maximum safety, thereby requiring little effort and expense for construction, and to attain higher speeds in straight sections of track.
The invention teaches that in a straight section of track, a speed differential of opposite track wheels is determined, a control output is determined by a controller as a function of a set point, and the frequency and the damping of the control output can be dynamically adjusted by controller parameters. In the ideal case, the set point is thereby zero. The torque set points for the torque-controlled individual-wheel drive systems are calculated from the required acceleration moment and the control output.
When the vehicle is negotiating curves, the angular position of the axle that can be fixed in position with regard to the underbody is adjusted so that the track wheels are tangent to the rails by adjusting the angular position of the axle by means of the torque set points of the individual wheel drives. The torque set points for the torque-controlled individual-wheel drives are calculated from the required acceleration torque and the control output determined by the controller. The controller thereby determines the set point from the curvature of the rails and the control output from the angular position of the axlexe2x80x94which corresponds to the actual measured value.
The curvature is thereby measured continuously, so that if it drops below a threshold value, the axle can be arrested in position, to guarantee quieter running on the straight sections of track.